The present invention generally relates to semiconductor devices and semiconductor device assembly, and, more particularly, to a substrate having a die attach area with a reservoir for receiving die attach adhesive.
Semiconductor dies are packaged before being attached to a printed circuit board (PCB) or other devices. The packaging protects the integrated circuit die from being contaminated, such as by water, dust or moisture. The packaging process includes attaching the die to a substrate or lead frame and electrically connecting bond pads on the die with corresponding electrical connection sites, e.g., lead fingers, such as with bond wires. The substrate electrical connection sites are electrically connected to I/O pads or other externally connectable pads, such as solder balls.
Before the die bond pads are electrically connected to the substrate connection sites, the die is mechanically attached to the substrate. Typically, a conductive paste or an epoxy adhesive is used to attach a die to a substrate. However, epoxy adhesive, even if filled with particles, has a tendency to spread or “bleed” away from the adhesion area (die attach area). Any filled epoxy or epoxy resin that flows onto a substrate connection site contaminates the site, which may compromise the ensuing wire bond.
Various methods for reducing resin bleed have been developed. For example, the substrate surface may have a recess at the point of attachment of the die, such that the die and adhesive will be recessed below the adjoining areas of the substrate where electrical bonding sites are located. U.S. Pat. No. 5,409,863 discloses a method for controlling adhesive spread during a die-attach process using a low-profile barrier, such as a solder mask ring, formed at a die attach area of a substrate. The barrier surrounds the die attach area, preventing the spread of adhesive resin onto the adjacent bonding sites on the substrate. While this method seems to work well, if the barrier is not sufficiently spaced from the die attach area, it may not permit enough adhesive to be used to securely attach the die to the substrate. On the other hand, spacing the barrier too far from the die attach area leads to usage of more adhesive than necessary.
It also has been suggested to treat the area surrounding the die attach area with fluorinated coupling agents or other surfactants to render the areas non-wettable to the adhesive resin. However, while these chemicals may prevent resin from adhering to areas surrounding the die attach area, there still may be adhesive bleed-off, resulting in wasted adhesive. Moreover, these processes must be carefully controlled and are time consuming and relatively expensive. Further, as IC complexity increases and more bond sites are needed, a large die attach area, made larger by having a barrier surrounding area, can adversely increase package size.
Accordingly, it would be desirable to provide a substrate that prevents die attach adhesive from spreading onto adjacent wire bond sites when assembling an integrated circuit package, yet does not increase overall package size nor unduly limit the amount of die attach adhesive used to attach the die to the substrate.